It is clear that, in Neurospora, the products of mitochondrial protein synthesis fall into four molecular weight groups based on acrylamide gel sizing (approximately 40,000, 30,000, 20,000 amd 10,000). The 10,000 molecular weight species disappears during a chase of two hours' duration (i.e., it is observed only for a short time immediately after synthesis). Proposed work for the next year consists almost entirely of protein chemistry on these four proteins. The primary questions will be to determine: 1) Whether the small subunit is a component of any of the larger ones--particularly the largest one, since it increases in size while the smaller one disappears during a chase; 2) Whether within each molecular weight one or more labelled proteins are present; 3) Whether the 30,000 MW labelled peak found in cytochrome oxidase, ATPase and succinate cytochrome C reductase are the same protein.